Recoil force attenuation is an ongoing concern in weapon design. For example, a shoulder-launched weapon in an open-ended launch tube traditionally uses either rocket propulsion or a powder charge with a countermass. Rocket propulsion operates by firing within the launcher tube, with the rocket exhaust exiting the open rear of the tube. The primary disadvantage of rocket propulsion is that a lethal zone is created behind the launcher by the combination of shock waves, rapidly moving hot gas, and high sound levels. Large smoke and flash discharge can be used to identify the position of the gunner. Accordingly, the above characteristics prevent the use of rocket systems within a confined space such as an enclosed fortification or bunker.
A variant of the rocket propulsion method is to fire the round out of the tube with a small charge, and then ignite the rocket when it is a safe distance from the gunner. The disadvantage of this method is that additional components (with potential failure mechanisms) are required. Additionally, guidance mechanisms must be incorporated into the round thereby increasing the cost and complexity of the system.
The powder-charge propulsion method operates by firing a powder charge within the launcher tube with the charge sandwiched between the round and a countermass. The round is fired out the front of the launcher tube while a countermass is discharged out the rear of the launcher tube. The disadvantage of the powder-charge method is that the countermass becomes a lethal projectile traveling rearward at high velocity thereby endangering anything in its path.
A variant of the power-charge propulsion method is the use of a frangible countermass which upon exiting the launch tube breaks up into small, lightweight pieces. These pieces slow down rapidly due to the high drag per unit mass. The discharge from the rear of the launcher tube remains dangerous at close range and the smoke and flash can be used to identify the position of the gunner.